Internal combustion engines, particularly diesel engines, utilize fuel injection systems for providing precise metering of fuel to each cylinder, thereby enhancing performance and fuel economy, as well as reduction of undesirable emissions.
A typical conventional application of a fuel injector 10 with respect to a diesel internal combustion engine 12 is shown at FIGS. 1 and 2. A source of pressurized fuel 14 is connected by a fuel line 16 to the fuel injector 10. As best seen at FIG. 2, the fuel injector 10 includes a tip body 18, a needle valve 20 including a needle 22 and valve seat 24, and a needle spring 26 which biases the needle seatably upon the valve seat. Pressurized fuel passes along a passage 28 of the fuel injector and upon a predetermined level of pressure being attained, the needle 22 moves against the biasing of the needle spring 26, thereby opening the needle valve seat 20, whereby fuel injects into the cylinder. When the pressurized fuel drops below a second predetermined level, the needle 22 is biased by the needle spring 26 so as to again close the needle valve 20. The movements of the needle 22 are very rapid, and when the needle closes upon the valve seat 24, a percussion occurs.
Engine performance, fuel economy and emissions all depend upon precise timing of the start and end of the fuel injection event. In this regard, it is desirable for the beginning and end of the fuel injection event to be as rapid as possible.
The closure percussion involves a tendency of the needle 22 to bounce at the valve seat 24, with the undesirable consequences of undue seat wear and a second fuel injection occurring during the bounce. The bounce induced fuel injection involves an unwanted low pressure fuel injection late in the combustion cycle which can adversely affect fuel economy and performance and increase undesirable emissions.
The origin of closure percussion bounce relates to the metallic components of the needle and the valve seat colliding in an essentially elastic manner. As such, there is a substantial conservation of kinetic energy which translates into bounce of the needle.
Conventionally, fuel injector manufacturers have struggled with needle bounce, and have attempted to solve this problem by incorporating hydraulic assist systems which serve to assuage needle bounce. Problematically, these hydraulic systems are complex and costly.
Accordingly, what is needed is a fuel injector needle valve in which the needle valve inherently has an absence of bounce.